The present invention relates to sintering plants for the sintering of fine grained iron ores and the like and specifically to the exhausting of gases from such plants.
It is known that fine grained iron ores must often be agglomerated into larger particles before they can be successfully used as a blast furnace feed. One method of effecting such agglomeration is to sinter the ore fines on a moving, continuous belt or grate. The mixture to be sintered is placed on the sintering machine, is ignited on its surface under an ignition hood and the ore is sintered as an oxygen-containing gas, usually air, is pulled through the mixture. As this air is pulled through the mixture, off-gases from the sintering process are caused to be exhausted to a point below the strand.
As sintering progresses, the combustion front moves progressively from the top of the mixture downward through the bed. When the front reaches the bottom of the grate, the sintering process is complete. This point is called the "burn-through" point. Subsequently it is necessary to cool the hot sinter. This cooling can be accomplished on the sinter machine itself, and for this purpose a cooling section may follow the sintering section.
As in the sintering section, air is pulled through the strand in the cooling section. The purpose of this air, rather than being to substain combustion, is to cool the sinter. Accordingly, it is found that air consumption per area unit in the sintering section and the cooling section differs. It is also found that there exists a variance in the permeability of the sinter bed between the sintering section and the cooling section. Additionally, while it is often considered advantageous to subject the off-gases from the sintering zone to a washing process in order to remove harmful substances from these gases, it may not be necessary to treat the cooling gases in this manner. It is, therefore, often advantageous to evacuate the gases from the sintering section and the cooling section through separate gas-collecting mains by means of separate gas evacuation fans.
From DE-AS 20 20 823 and DE-AS 23 21 213 it is known that exhaust gases from the sintering section from one side of the sintering belt can be drawn from one side of the sintering strand through wind boxes into a gas-collecting main arranged next to the sinter belt. These patents also disclose removing the dust generated in the sinter process in an electrostatic gas-cleaning system which is located at the feed end of the sintering machine, and to then lead the sintering section exhaust gases to a flue. The exhaust gas from the cooling section is also exhausted on one side from the wind boxes in the cooling section and is passed into a second gas-collecting main located next to the sinter machine. The dust is then removed in cyclones and the gas is brought into a flue located next to the sinter machine. For this process two flues are required and efficient gas evacuation, because of the unilateral means of exhaust, especially in the cooling section, is possible only with narrow sintering machines.
A similar process is described in British patent specification No. 1,427,089. There, the gas collecting mains are arranged in tandem and are exhausted in opposite directions. With this arrangement, either two flues or very long connecting lines to a single flue are required.
In U.S. Pat. No. 3,816,096 the option is presented of either connecting the last wind boxes of the sintering zone to the gas-collecting main of the cooling zone or the first wind boxes of the cooling zone to the gas collecting main of the sintering zone.
From U.S. Pat. No. 3,831,911 it is known to exhaust the exhaust gases of the cooling and the sintering sections unilaterally through two side-by-side gas-collecting mains, in which both gas-collecting mains run in the direction of the feed end of the sinter machine. In this design, the disadvantage of unilateral exhaust is also present.
From U.S. Pat. No. 2,441,383 it is known to exhaust the exhaust gases from the cooling and the sintering zones unilaterally into two gas-collecting mains located next to the sintering machine. One connecting pipe then leads from the centers of these gas-collecting mains to a fan and then to a flue. Here also the disadvantages associated with unilateral exhaust are present, and either two flues or excessively long gas mains are required. The object of the present invention is to provide a sintering plant where separate gas collecting systems are provided for the cooling section and for the sintering section and where gases are efficiently evacuated from the wind boxes while structural layout, space requirements, and accessibility are maintained at optimum conditions. The present invention allows such efficient evacuation by providing for the exhaust of the wind boxes underlying the cooling zone of the sinter machine from two sides of those wind boxes.